The present invention relates to pressure applicator devices for applying a predetermined static pressure to a body part of a patient. The invention is particularly useful as a probe for application to a digit (ie., a finger or toe) of a patient for the non-invasive detection of certain medical conditions in accordance with the method described in our PCT Application PCT/IL97/00249; and the invention is therefore described below especially with respect to such applications.
Our Application PCT/IL97/00249 (WO98/04182, published Feb. 5, 1998 which is incorporated by reference as if fully set forth herein) discloses methods and apparatus for the non-invasive detection of a change in a physiological condition of a patient by monitoring changes in the peripheral arterial tone as manifested by changes in the arterial blood volume in a terminal extremity of a body part, preferably a digit (finger or toe) of the patient. The method and apparatus are described in that application particularly for detecting mycardial ischemia and sleep apnea, and also for the continuous monitoring of blood pressure. The described apparatus includes a probe for application to the patient""s body part (e.g., finger) which probe includes a housing for receiving the distal end of the patient""s body part, and pressurizing means for applying a static pressure field substantially uniformly around the distal end of the patient""s body part when received in the compartment, including its terminal-most extremity. The static pressure field is of a predetermined magnitude sufficient to substantially prevent distention of the venous vasculature, uncontrolled venous backflow, and retrograde shockwave propagation into the distal end of the body part, and to partially unload the wall tension of, but not to occlude, the arteries in the distal end of the body part when at heart level or below. The probe further includes a sensor within the housing for sensing changes in the distal end of the patient""s body part related to changes in volume therein due to changes in instantaneous blood volume related to arterial tone.
That application described a number of probe constructions in which the static pressure field was applied via a remotely located pressure source connected by tubing to a fluid chamber within the probe. However, utilizing such remotely-located pressure sources complicates the construction of the apparatus and also restricts the mobility of the patient.
An object of the present invention is to provide a device particularly useful as a probe in the method and apparatus of the above-cited PCT Application but of a simplified or improved construction as compared to the devices described therein. Another object is to provide a probe which does not restrict the mobility of the patient.
According to broad aspect of the present invention, there is provided a device for application to a digit of a patient to detect a change in the physical condition of the patient; the device comprising a probe including: a housing defining a compartment closed at one end and open at the opposite end for receiving the distal end of the patient""s body part; pressurizing means for applying a static pressure field substantially uniformly around the distal end of the patient""s body part, when received in the compartment, including the extreme distal tip of the patient""s body part, which static pressure field is of a predetermined magnitude sufficient to substantially prevent distention of the venous vasculature, uncontrolled venous backflow, and retrograde venous shockwave propagation into the distal end, and to partially unload the wall tension of, but not to occlude, the arteries in the distal end when at heart level or below; and a sensor for sensing changes in the distal end of the patient""s body part related to changes in volume thereof due to changes in instantaneous blood volume related to arterial blood volume therein; characterized in that the pressurizing means for applying the static pressure substantially uniformly around the distal end of the patient""s body part, including its terminal-most extremity, is constituted of a medium wholly self-contained within the probe.
A number of embodiments are described below for purposes of example.
According to further features in one class of embodiments described below, the pressurizing means includes an inner resilient membrane within the housing and defining therewith an inner chamber to be filled with a fluid for applying the static pressure via the membrane substantially uniformly around the distal end of the patient""s body part, including its terminal-most extremity.
According to further features in the latter described embodiments, the pressurizing means further includes an outer resilient membrane attached to the housing externally thereof and defining therewith an outer chamber communicating with the inner chamber via openings in the housing for enlarging the effective volume of the inner chamber such as to cause the inner membrane to apply substantially the same static pressure around the distal end of the patient""s body part despite changes in volume therein.
A further embodiment is described below for purposes of example, wherein the pressure means includes a body of resilient sponge material formed with a recess defining the compartment for receiving the patient""s body part when inserted therein.
The sensor within the housing is described below, for purposes of example, as being either an optical sensor for optically detecting, or a Hall Effect sensor for magnetically detecting, volume changes in the subject""s finger which attend pulse-related blood volume changes and corresponding finger girth changes.
As will be described more particularly below, the present invention enables probes to be constructed with the static pressurizing means wholly self-contained within the probe housing, thereby greatly simplifying the construction of the probe as well as reducing restrictions on the mobility of the patient using such a probe. However, the invention may also be implemented in a two-section probe wherein one section includes a first housing attached to the body part and defining a part of the static pressurizing means, and the second section includes a second housing having another part of the static pressurizing means in fluid connection to the first section, the sensor being located within the second section.
While the invention is particularly useful in the methods and apparatus of the above-cited PCT Application, the invention, or various features thereof, can be used in other applications as will also be described below.
Further features and advantages of the invention will be apparent from the description below.